Two opposite signal transducing mechanisms regulate a G-protein-coupled guanylyl cyclase.
Membrane-bound guanylyl cyclase (GC) is regulated by muscarinic receptors (mAChRs). Carbamylcholine (CC) induces a "dual" biological response on GC activity. Thus, an activation is observed at 0.1 nM and a maximal response at 1 nM CC. However, at higher agonist concentration (> 100 nM), there is an agonist-dependent inhibition of GC. This CC dual response is affected by 4-DAMP and HDD (M3 antagonists), which produce a right-shift of the CC curve; the maximal CC dose response with 4-DAMP is more potent than that with HDD. Moreover, AFDX-DS (an M2 antagonist) increases basal activity and decreases the agonist-dependent inhibition. Neither the CC response nor the CC maximal dose responses are affected by pirenzepine (PZ, M1 antagonist). The agonist-dependent stimulation of GC activity is inhibited by 4-DAMP showing a -log IC50 = 8.4 +/- 0.4, while AFDX116 DS poorly inhibits such activity with a -log IC50 = 5.0 +/- 0.2. The agonist-independent (basal) GC activity also was inhibited by 4-DAMP, in a dose-dependent manner, with an IC50 = 8.5 +/- 0.2. Nonetheless, other muscarinic antagonists (PZ and HDD) were not able to inhibit this basal GC. Pertussis toxin treatment produces a complete blockade of the agonist-dependent inhibition of GC with a full expression of the agonist-dependent activation of membrane-bound GC. These results indicate that membrane-bound GC is regulated by muscarinic agents through two opposite signaling pathways; one involves the activation of GC via an M3 mAchR coupled to a PTX-insensitive G protein, while the GC inhibition is mediated through a PTX-sensitive Gi/o protein possibly coupled to an M2 mAChR.
Alfonzo
M J
MJ
Sección de Biomembranas, Facultad de Medicína, Universidad Central de Venezuela, Caracas, Venezuela. hmag5@telcel.net.ve
de Becemberg
I L
IL
de Villaroel
S S
SS
de Herrera
V N
VN
Misle
A J
AJ
de Alfonzo
R G
RG
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006162:Guanylate Cyclase / Q000378:metabolism*; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism; D037342:Pertussis Toxin; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D014132:Trachea / Q000166:cytology / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010880:Piperidines; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D010890:Pirenzepine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D006162:Guanylate Cyclase; C048593:otenzepad